A known developing device includes a toner storing portion formed with a replenishing port in an upper portion, and a toner cartridge detachably attached to the developing device above the toner storing portion. The toner storing portion is configured to store toner to be supplied to a developing roller. In the developing device, toner stored in the toner cartridge is supplied into the toner storing portion as it falls down into the toner storing portion via the replenishing port.
The developing device further includes an agitating member that is configured to agitate toner supplied to the toner storing portion. Toner supplied to the toner storing portion is agitated by the agitating member, and moved between the inside and outside of the toner storing portion in the vicinity of the replenishing port, and may be leaked outside from between the developing device and the toner cartridge. When the agitating member has a flexible agitating blade that is configured to agitate toner in sliding contact with the inner surface of the toner storing portion, the agitating blade contacts the inner surface at its free end being warped while sliding on the inner surface. When the warped agitating blade arrives at the replenishing port, the agitating blade is fully extended, and toner remaining on a front surface of the agitating blade with respect to the rotation direction of the agitating member is flung outside, which may lead to toner leakage.